Abstract:

It is an object to provide a method for manufacturing a liquid crystal
display device including a liquid crystal layer which exhibits a stable
blue phase. The following steps are performed: a first step of forming a
thermosetting first sealant so as to form a frame over a first substrate;
a second step of forming a photocurable and thermosetting second sealant
on an outer side than the first sealant over the first substrate; a third
step of dropping a liquid crystal material which exhibits a blue phase at
a given temperature on an inner side than the first sealant; a fourth
step of attaching a second substrate to the first substrate in a
reduced-pressure atmosphere; a fifth step of performing polymer
stabilization treatment on the liquid crystal material; and a sixth step
of curing the first sealant through heat treatment.

Claims:

1. A method for manufacturing a liquid crystal display device, comprising
the steps of:a first step of forming a first sealant so as to form a
frame over a first substrate;a second step of forming a second sealant on
an outer side than the first sealant over the first substrate;a third
step of dropping a liquid crystal material on an inner side than the
first sealant;a fourth step of attaching a second substrate to the first
substrate in a reduced-pressure atmosphere;a fifth step of performing
polymer stabilization treatment on the liquid crystal material; anda
sixth step of curing the first sealant through heat treatment,wherein the
first sealant is a thermosetting sealant, andwherein the second sealant
is a photocurable and thermosetting sealant.

2. The method for manufacturing a liquid crystal display device according
to claim 1, further comprising the step of pre-curing the first sealant
through heat treatment in a period between the first step and the second
step.

3. The method for manufacturing a liquid crystal display device according
to claim 1, wherein as the liquid crystal material, a material which
exhibits a blue phase at a given temperature is used.

4. The method for manufacturing a liquid crystal display device according
to claim 1, wherein the polymer stabilization treatment is performed in
such a manner that heat treatment is performed so that a temperature of
the liquid crystal material is set to a temperature at which the liquid
crystal material exhibits a blue phase, and then the liquid crystal
material is irradiated with ultraviolet rays.

5. The method for manufacturing a liquid crystal display device according
to claim 1, wherein the polymer stabilization treatment is performed in
such a manner that heat treatment is performed so that a temperature of
the liquid crystal material is set to a temperature within +5.degree. C.
of a phase transition temperature between a blue phase and an isotropic
phase, at which the liquid crystal material exhibits an isotropic phase,
and then the liquid crystal material is irradiated with ultraviolet rays.

6. The method for manufacturing a liquid crystal display device according
to claim 1, wherein the liquid crystal material includes a photocurable
resin.

7. A method for manufacturing a liquid crystal display device, comprising
the steps of:a first step of forming a first sealant so as to form a
frame over a first substrate;a second step of forming a second sealant on
an outer side than the first sealant over the first substrate;a third
step of dropping a liquid crystal material on an inner side than the
first sealant;a fourth step of attaching a second substrate to the first
substrate in a reduced-pressure atmosphere;a fifth step of curing the
first sealant through heat treatment; anda sixth step of performing
polymer stabilization treatment on the liquid crystal material,wherein
the first sealant is a thermosetting sealant, andwherein the second
sealant is a photocurable and thermosetting sealant.

8. The method for manufacturing a liquid crystal display device according
to claim 7, further comprising the step of cutting the first substrate
and the second substrate between the first sealant and the second sealant
in a period between the fifth step and the sixth step.

9. The method for manufacturing a liquid crystal display device according
to claim 7, further comprising the step of pre-curing the first sealant
through heat treatment in a period between the first step and the second
step.

10. The method for manufacturing a liquid crystal display device according
to claim 7, wherein as the liquid crystal material, a material which
exhibits a blue phase at a given temperature is used.

11. The method for manufacturing a liquid crystal display device according
to claim 7, wherein the polymer stabilization treatment is performed in
such a manner that heat treatment is performed so that a temperature of
the liquid crystal material is set to a temperature at which the liquid
crystal material exhibits a blue phase, and then the liquid crystal
material is irradiated with ultraviolet rays.

12. The method for manufacturing a liquid crystal display device according
to claim 7, wherein the polymer stabilization treatment is performed in
such a manner that heat treatment is performed so that a temperature of
the liquid crystal material is set to a temperature within +5.degree. C.
of a phase transition temperature between a blue phase and an isotropic
phase, at which the liquid crystal material exhibits an isotropic phase,
and then the liquid crystal material is irradiated with ultraviolet rays.

13. The method for manufacturing a liquid crystal display device according
to claim 7, wherein the liquid crystal material includes a photocurable
resin.

14. A method for manufacturing a liquid crystal display device, comprising
the steps of:a first step of forming a sealant so as to form a frame over
a first substrate;a second step of pre-curing the sealant through
irradiation with ultraviolet rays;a third step of dropping a liquid
crystal material on an inner side than the sealant;a fourth step of
attaching a second substrate to the first substrate in a reduced-pressure
atmosphere;a fifth step of performing polymer stabilization treatment on
the liquid crystal material; anda sixth step of post-curing the sealant
through heat treatment,wherein the sealant is a photocurable and
thermosetting sealant.

15. The method for manufacturing a liquid crystal display device according
to claim 14, wherein as the liquid crystal material, a material which
exhibits a blue phase at a given temperature is used.

16. The method for manufacturing a liquid crystal display device according
to claim 14, wherein the polymer stabilization treatment is performed in
such a manner that heat treatment is performed so that a temperature of
the liquid crystal material is set to a temperature at which the liquid
crystal material exhibits a blue phase, and then the liquid crystal
material is irradiated with ultraviolet rays.

17. The method for manufacturing a liquid crystal display device according
to claim 14, wherein the polymer stabilization treatment is performed in
such a manner that heat treatment is performed so that a temperature of
the liquid crystal material is set to a temperature within +5.degree. C.
of a phase transition temperature between a blue phase and an isotropic
phase, at which the liquid crystal material exhibits an isotropic phase,
and then the liquid crystal material is irradiated with ultraviolet rays.

18. The method for manufacturing a liquid crystal display device according
to claim 14, wherein the liquid crystal material includes a photocurable
resin.

19. A method for manufacturing a liquid crystal display device, comprising
the steps of:a first step of forming a sealant so as to form a frame over
a first substrate;a second step of pre-curing the sealant through
irradiation with ultraviolet rays;a third step of dropping a liquid
crystal material on an inner side than the sealant;a fourth step of
attaching a second substrate to the first substrate in a reduced-pressure
atmosphere;a fifth step of post-curing the sealant through heat
treatment; anda sixth step of performing polymer stabilization treatment
on the liquid crystal material,wherein the sealant is a photocurable and
thermosetting sealant.

20. The method for manufacturing a liquid crystal display device according
to claim 19, wherein as the liquid crystal material, a material which
exhibits a blue phase at a given temperature is used.

21. The method for manufacturing a liquid crystal display device according
to claim 19, wherein the polymer stabilization treatment is performed in
such a manner that heat treatment is performed so that a temperature of
the liquid crystal material is set to a temperature at which the liquid
crystal material exhibits a blue phase, and then the liquid crystal
material is irradiated with ultraviolet rays.

22. The method for manufacturing a liquid crystal display device according
to claim 19, wherein the polymer stabilization treatment is performed in
such a manner that heat treatment is performed so that a temperature of
the liquid crystal material is set to a temperature within +5.degree. C.
of a phase transition temperature between a blue phase and an isotropic
phase, at which the liquid crystal material exhibits an isotropic phase,
and then the liquid crystal material is irradiated with ultraviolet rays.

23. The method for manufacturing a liquid crystal display device according
to claim 19, wherein the liquid crystal material includes a photocurable
resin.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to a liquid crystal display device and
a method for manufacturing the liquid crystal display device.

[0003]2. Description of the Related Art

[0004]In recent years, display devices (flat panel display) which are very
thin and lightweight as compared to cathode-ray tube display devices have
developed. The flat panel displays include liquid crystal display devices
which have liquid crystal elements, electro-luminescent (EL) display
devices which have self-light emitting elements such as EL elements,
plasma displays, and the like, and they are in competition in the market.

[0005]Although each kind of flat panel display has good points and bad
points as of now, the liquid crystal display devices are inferior to the
other flat panel displays in the response time of an element (the speed
of switching the display). Various techniques for overcoming the
disadvantage in the response time have been proposed so far. A
conventional liquid crystal element which employs a driving method of a
liquid crystal called a twisted nematic (TN) mode has a response time of
approximately 10 milliseconds, whereas a liquid crystal element which
employs an optical compensated birefringence (OCB) mode or a
ferroelectric liquid crystal (FLC) mode has realized an improved response
time of approximately 1 millisecond (see Patent Document 1, for example).

[0006]Another technique which attracts as much attention as such a driving
method of a liquid crystal uses a state called a blue phase for a liquid
crystal display element. The blue phase is a liquid crystal phase which
appears between a chiral nematic phase having a relatively short spiral
pitch and an isotropic phase, and has a feature of an extremely short
response time. The liquid crystal display element using a liquid crystal
layer which exhibits the blue phase does not need to have an orientation
film and can widen a viewing angle and thus is expected to be put into
practical use. However, the blue phase is exhibited in a small
temperature range of 1° C. to 3° C. between a cholesteric
phase and an isotropic phase. Thus, there is a problem in that the
temperature of the element needs to be controlled precisely.

[0007]In order to solve this problem, it is proposed that the temperature
range of the blue phase be widened by polymer stabilization treatment
(see Patent Document 2, for example). The polymer stabilization treatment
is performed in such a manner that a photocurable resin is mixed into a
liquid crystal material and light irradiation is performed at a
temperature at which the blue phase is exhibited.

[0009]In the case where a liquid crystal display device is manufactured
using a liquid crystal dropping method (one drop fill (ODF) method), it
is desirable that a sealant with a high viscosity be used in order to
keep adhesion between substrates after attachment (to keep a vacuum state
in a sealant area). In general, polymer stabilization treatment is
performed in such a manner that with the use of a photocurable and
thermosetting sealant with a high viscosity, a substrate on which a
liquid crystal is dropped is attached to another substrate in a
reduced-pressure atmosphere, the sealant is then irradiated with
ultraviolet rays to be pre-cured, and then heat treatment is performed to
post-cure the sealant and a liquid crystal material is irradiated with
ultraviolet rays.

[0010]However, in the case where a photocurable and thermosetting sealant
is irradiated with ultraviolet rays to be pre-cured before polymer
stabilization treatment, a liquid crystal material which is formed on an
inner side than the sealant is also irradiated with ultraviolet rays.
Accordingly, polymer stabilization treatment is performed when the liquid
crystal material exhibits a phase at a room temperature. For example, in
the case where the liquid crystal material exhibits a cholesteric phase
at a room temperature, polymer stabilization treatment is performed on a
part of the liquid crystal material which is irradiated with ultraviolet
rays in a cholesteric phase. Therefore, there is a problem in that a
liquid crystal layer which exhibits a stable blue phase cannot be formed.

[0011]In addition, at this time, even in the case where a light shielding
mask is formed to prevent the liquid crystal material from being
irradiated with ultraviolet rays, there is a concern that the liquid
crystal material might be irradiated with light reflected from wirings
formed over a substrate and the like.

[0012]On the other hand, in the case where polymer stabilization treatment
is performed on a liquid crystal material before a photocurable and
thermosetting sealant is irradiated with ultraviolet rays, the viscosity
of the sealant is reduced due to increase in the temperature in the
polymer stabilization treatment, which causes a problem in that the width
of the sealant which is in contact with the liquid crystal material is
increased.

[0013]It is an object of an embodiment of the disclosed invention to
provide a liquid crystal display device including a liquid crystal layer
which exhibits a stable blue phase. It is another object of an embodiment
of the disclosed invention to provide a liquid crystal display device in
which even when polymer stabilization treatment is performed, in the case
of employing a liquid crystal dropping method using a photocurable and
thermosetting sealant, increase in the width of the sealant for sealing a
liquid crystal material is suppressed, and a liquid crystal layer which
exhibits a stable blue phase is included. In addition, it is another
object of an embodiment of the disclosed invention to provide a liquid
crystal display device including a liquid crystal layer capable of
high-speed response.

[0014]An embodiment of the disclosed invention is that when a liquid
crystal display device including a blue phase liquid crystal layer is
manufactured using a liquid crystal dropping method (an ODF method),
irradiation of a liquid crystal material with unintended light before
polymer stabilization treatment is performed on a liquid crystal layer is
suppressed.

[0015]Another embodiment of the disclosed invention includes: a first step
of forming a thermosetting first sealant so as to form a frame over a
first substrate; a second step of forming a photocurable and
thermosetting second sealant on an outer side than the first sealant over
the first substrate; a third step of dropping a liquid crystal material
on an inner side than the first sealant; a fourth step of attaching a
second substrate to the first substrate in a reduced-pressure atmosphere;
a fifth step of performing polymer stabilization treatment on the liquid
crystal material; and a sixth step of curing the first sealant through
heat treatment. Note that another step may be included in a period
between the first step and the sixth step.

[0016]Another embodiment of the disclosed invention includes: a first step
of forming a thermosetting first sealant so as to form a frame over a
first substrate; a second step of forming a photocurable and
thermosetting second sealant on an outer side than the first sealant over
the first substrate; a third step of dropping a liquid crystal material
on an inner side than the first sealant; a fourth step of attaching a
second substrate to the first substrate in a reduced-pressure atmosphere;
a fifth step of curing the first sealant through heat treatment; and a
sixth step of performing polymer stabilization treatment on the liquid
crystal material. Note that another step may be included in a period
between the first step and the sixth step.

[0017]Another embodiment of the disclosed invention includes: a first step
of forming a photocurable and thermosetting sealant so as to form a frame
over a first substrate; a second step of pre-curing the sealant through
irradiation with ultraviolet rays; a third step of dropping a liquid
crystal material on an inner side than the sealant; a fourth step of
attaching a second substrate to the first substrate in a reduced-pressure
atmosphere; a fifth step of performing polymer stabilization treatment on
the liquid crystal material; and a sixth step of post-curing the sealant
through heat treatment. Note that another step may be included in a
period between the first step and the sixth step.

[0018]Another embodiment of the disclosed invention includes: a first step
of forming a photocurable and thermosetting sealant so as to form a frame
over a first substrate; a second step of pre-curing the sealant through
irradiation with ultraviolet rays; a third step of dropping a liquid
crystal material on an inner side than the sealant; a fourth step of
attaching a second substrate to the first substrate in a reduced-pressure
atmosphere; a fifth step of post-curing the sealant through heat
treatment; and a sixth step of performing polymer stabilization treatment
on the liquid crystal material. Note that another step may be included in
a period between the first step and the sixth step.

[0019]According to an embodiment of the disclosed invention, a material
which exhibits a blue phase at a given temperature is used as the liquid
crystal material.

[0020]According to another embodiment of the disclosed invention, the
polymer stabilization treatment can be performed in such a manner that
heat treatment is performed so that the temperature of the liquid crystal
material is set to a temperature at which the liquid crystal material
exhibits a blue phase, and then the liquid crystal material is irradiated
with ultraviolet rays. Alternatively, the polymer stabilization treatment
may be performed in such a manner that heat treatment is performed so
that the temperature of the liquid crystal material is set to a
temperature within +5° C. of a phase transition temperature
between a blue phase and an isotropic phase, at which the liquid crystal
material exhibits an isotropic phase, and then the liquid crystal
material is irradiated with ultraviolet rays.

[0021]Note that a liquid crystal display device in this specification
means an image display device, a display device, or a light source
(including a lighting device). Furthermore, the liquid crystal display
device also includes all of the following modules in its category: a
module to which a connector such as a flexible printed circuit (FPC), a
tape automated bonding (TAB) tape, or a tape carrier package (TCP) is
attached; a module having a TAB tape or a TCP at the tip of which a
printed wiring board is provided; and a module in which an integrated
circuit (IC) is directly mounted on a display element by a chip on glass
(COG) method.

[0022]According to another embodiment of the disclosed invention, a
photocurable and thermosetting second sealant is formed on an outer side
than a thermosetting first sealant and made to serve for improvement of
adhesion between substrates, whereby irradiation with ultraviolet rays
for pre-curing the second sealant is not needed. Accordingly, a liquid
crystal display device including a liquid crystal layer which exhibits a
stable blue phase can be manufactured. Moreover, even in the case where
polymer stabilization treatment is performed before the photocurable and
thermosetting second sealant is irradiated with ultraviolet rays, when a
thermosetting sealant is used as the first sealant which is in contact
with the liquid crystal layer and the photocurable and thermosetting
second sealant is formed on an outer side than the first sealant,
adhesion between the substrates can be kept and increase in the width of
the sealant which is in contact with the liquid crystal layer can be
suppressed.

[0023]According to another embodiment of the disclosed invention, even
when a liquid crystal dropping method is performed using a photocurable
and thermosetting sealant, the sealant is irradiated with ultraviolet
rays to be pre-cured before formation of the liquid crystal material,
whereby the liquid crystal material can be prevented from being
irradiated with unintended light. Accordingly, a liquid crystal display
device including a liquid crystal layer which exhibits a stable blue
phase can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]In the accompanying drawings:

[0025]FIGS. 1A to 1F are views illustrating an example of a method for
manufacturing a liquid crystal display device;

[0026]FIGS. 2A to 2F are views illustrating an example of a method for
manufacturing a liquid crystal display device;

[0027]FIGS. 3A to 3F are views illustrating an example of a method for
manufacturing liquid crystal display devices;

[0028]FIGS. 4A to 4F are views illustrating an example of a method for
manufacturing a liquid crystal display device;

[0029]FIGS. 5A to 5F are views illustrating an example of a method for
manufacturing liquid crystal display devices;

[0035]FIGS. 11A to 11F are views illustrating an example of a method for
manufacturing liquid crystal display devices;

[0036]FIGS. 12A to 12G are views illustrating an example of a method for
manufacturing liquid crystal display devices; and

[0037]FIGS. 13A and 13B are views illustrating an example of a method for
manufacturing a liquid crystal display device.

DETAILED DESCRIPTION OF THE INVENTION

[0038]Embodiments of the present invention will be described below with
reference to the accompanying drawings. Note that the present invention
is not limited to the following description of the embodiments, and it is
readily appreciated by those skilled in the art that modes and details of
the present invention can be modified in a variety of ways without
departing from the scope and spirit of the present invention.
Accordingly, the present invention should not be interpreted as being
limited to the following description of the embodiments. Further,
structures according to different embodiments can be implemented in
combination as appropriate. Note that in the structure of the present
invention described below, reference numerals indicating the same
portions and portions having a similar function are used in common in
different drawings, and repeated descriptions thereof are omitted.

Embodiment 1

[0039]In this embodiment, an example of a method for manufacturing a
liquid crystal display device is described with reference to drawings.

[0040]First, a first substrate 100 is prepared, and a first sealant 102 is
formed over the first substrate 100 (see FIG. 1A).

[0041]As the first substrate 100, glass substrates used for electronics
industry (also called a "non-alkali glass substrate") such as an
aluminosilicate glass substrate, an aluminoborosilicate glass substrate,
or a barium borosilicate glass substrate; a quartz substrate; a ceramic
substrate; a plastic substrate; or the like can be used. An element such
as a transistor for forming a pixel and the like of a liquid crystal
display device may be provided over the substrate.

[0042]The first sealant 102 can be formed using a thermosetting resin. The
thermosetting resin is a resin cured by heat treatment. For the
thermosetting resin, an epoxy-based resin, an acrylate-based (urethane
acrylate) resin, or the like can be used. A filler may be mixed into the
first sealant 102. In addition, spacers may be dispersed before formation
of the first sealant 102.

[0043]Moreover, the first sealant 102 may be formed so as to form a frame
(closed-loop shape). Here, a case where the first sealant 102 is formed
so as to form a frame with a rectangular shape is described. Note that
the frame shape of the first sealant 102 is not limited to the
rectangular shape, and the first sealant 102 may be formed so as to form
a frame with a circular shape, an elliptical shape, a polygonal shape
other than a rectangular shape, or the like.

[0044]Furthermore, after the first sealant 102 is formed over the first
substrate 100, the first sealant 102 may be pre-cured through heat
treatment. By pre-curing the first sealant 102, mixture of an impurity
into a liquid crystal from the first sealant 102 can be suppressed when
the liquid crystal is in contact with the first sealant 102 later.

[0045]Next, a second sealant 104 is formed on an outer side than the first
sealant 102 over the first substrate 100, and a liquid crystal material
106 is dropped on an inner side than the first sealant 102 (on an inner
side than the frame of the first sealant 102) (see FIG. 1B). The second
sealant 104 may be formed apart from the first sealant 102.

[0046]The second sealant 104 can be formed using a photocurable and
thermosetting resin. The photocurable and thermosetting resin is
pre-cured by light irradiation and then post-cured by heat treatment. As
the photocurable and thermosetting resin, a resin in which an
acrylic-based resin and an epoxy-based resin are mixed can be used.
Further, a UV initiator, a thermosetting agent, a coupling agent, or the
like may be mixed into the resin. Furthermore, a filler may be mixed into
the second sealant 104.

[0047]The second sealant 104 serves for improvement of adhesion between
substrates at the time of attachment of the substrates, which is
performed later. Therefore, the viscosity of a resin used for the second
sealant 104 is made higher than that of the resin used for the first
sealant 102. As the second sealant 104, a resin with a viscosity of
greater than or equal to 200 Pasec (25° C.) and less than or equal
to 450 Pasec (25° C.) is preferably used and a resin with a
viscosity of greater than or equal to 250 Pasec (25° C.) and less
than or equal to 400 Pasec (25° C.) is more preferably used. Here,
the term "viscosity" means a viscosity before another substrate is
attached to the first substrate 100. In addition, the viscosity of the
sealant can be measured with any one of a rotational viscometer, a
falling sphere viscometer, and a capillary viscometer.

[0048]The second sealant 104 can surround the first sealant 102 and form a
frame. The second sealant 104 is formed so as to surround the first
sealant 102, whereby adhesion between substrates can be improved
effectively. Here, a case where the second sealant 104 is formed so as to
form a frame with a rectangular shape as in the first sealant 102 is
described; however, the frame shape of the second sealant 104 is not
limited to the rectangular shape, and the second sealant 104 may be
formed so as to form a frame with a circular shape, an elliptical shape,
a polygonal shape other than a rectangular shape, or the like.

[0049]As the liquid crystal material 106, a liquid crystal material which
exhibits a blue phase can be used. The liquid crystal material which
exhibits a blue phase includes a liquid crystal, a chiral agent, a
photocurable resin, and a photopolymerization initiator. The chiral agent
is used to align the liquid crystal in a helical structure and to make
the liquid crystal exhibit a blue phase. As an example, a liquid crystal
material into which a chiral agent is mixed at 5 wt % or more can be
used. As the liquid crystal, a thermotropic liquid crystal, a
low-molecular liquid crystal, a high-molecular liquid crystal, a
ferroelectric liquid crystal, an anti-ferroelectric liquid crystal, or
the like can be used. Note that the liquid crystal material which
exhibits a blue phase does not need to exhibit a blue phase at the time
when the liquid crystal material is dropped over the first substrate 100,
and any liquid crystal material can be used as the liquid crystal
material which exhibits a blue phase as long as it exhibits a blue phase
at a given temperature by control of the temperature.

[0050]Note that FIG. 1B illustrates a case where one droplet of the liquid
crystal material 106 is dropped on an inner side than the first sealant
102 (an ODF method). Note that the method is not limited to such a
method, and a plurality of droplets of the liquid crystal material 106
may be dropped at appropriate places on an inner side than the first
sealant 102, and an appropriate amount of the liquid crystal material may
be dropped.

[0051]In FIG. 1B, the order of steps of forming the second sealant 104 and
dropping the liquid crystal material 106 is not limited; however, it is
preferable that the second sealant 104 be formed and then the liquid
crystal material 106 be dropped.

[0052]Next, the first substrate 100 and a second substrate 108 are
attached to each other (see FIG. 1C). The first substrate 100 can be
attached to the second substrate 108 with the use of the first sealant
102 and the second sealant 104.

[0053]When the first substrate 100 and the second substrate 108 are
attached to each other, the dropped liquid crystal material 106 spreads
over the substrate surface; thus, a liquid crystal layer 110 is formed.
The viscosity of the liquid crystal material 106 is high because the
liquid crystal material 106 includes a chiral agent. Accordingly, the
liquid crystal layer 110 does not necessarily spread over the entire
surface on an inner side than the first sealant 102 (the liquid crystal
layer 110 is not necessarily in contact with the first sealant 102) at
the stage of FIG. 1C.

[0054]As the second substrate 108, as in the first substrate 100, glass
substrates used for electronics industry such as an aluminosilicate glass
substrate, an aluminoborosilicate glass substrate, or a barium
borosilicate glass substrate; a quartz substrate; a ceramic substrate; a
plastic substrate; or the like can be used.

[0055]In addition, the first substrate 100 and the second substrate 108
are preferably attached to each other in a reduced-pressure atmosphere.
This is because when the substrates are attached to each other in a
reduced-pressure atmosphere, even if the substrates are exposed to the
atmosphere after attachment, a vacuum state can be kept on an inner side
than the sealant and the liquid crystal can finally spread to end
portions of the sealant (the liquid crystal can be formed in contact with
the sealant).

[0056]Next, polymer stabilization treatment is performed on the liquid
crystal layer 110 to form a liquid crystal layer 112 (see FIG. 1D).

[0057]The polymer stabilization treatment can be performed in such a
manner that a liquid crystal material including a liquid crystal, a
chiral agent, a photocurable resin, and a photopolymerization initiator
is irradiated with light having a wavelength with which the photocurable
resin and the photopolymerization initiator are reacted. In this
embodiment, the polymer stabilization treatment is performed in such a
manner that the temperature of the liquid crystal layer 110 is controlled
and the liquid crystal layer 110 in a state of exhibiting a blue phase is
irradiated with light.

[0058]However, the polymer stabilization treatment is not limited to this
manner and may be performed in such a manner that the liquid crystal
layer 110 in a state of exhibiting an isotropic phase at a temperature
within +10° C., preferably +5° C. of the phase transition
temperature between the blue phase and the isotropic phase is irradiated
with light. The phase transition temperature between a blue phase and an
isotropic phase refers to a temperature at which the phase transfers from
a blue phase to an isotropic phase when the temperature is raised or a
temperature at which the phase transfers from an isotropic phase to a
blue phase when the temperature is decreased.

[0059]As an example of the polymer stabilization treatment, after the
liquid crystal layer 110 is heated to exhibit an isotropic phase, the
temperature of the liquid crystal layer 110 can be gradually decreased so
that the phase transfers to a blue phase, and then, light irradiation can
be performed while the temperature at which the blue phase is exhibited
is kept. Alternatively, after the phase transfers to an isotropic phase
by gradually heating the liquid crystal layer 110, the liquid crystal
layer 110 at a temperature within +10° C., preferably +5°
C. of the phase transition temperature between a blue phase and an
isotropic phase (in a state of exhibiting an isotropic phase) can be
irradiated with light. In the case of using an ultraviolet curable resin
(a UV curable resin) as the photocurable resin included in the liquid
crystal material, the liquid crystal layer 110 may be irradiated with
ultraviolet rays.

[0060]Further, the polymer stabilization treatment can be performed in the
air atmosphere. In this case, the first substrate 100 and the second
substrate 108 are attached to each other in a reduced-pressure atmosphere
and then the reduced pressure state is changed to be an air atmosphere
state (the substrates are exposed to the atmosphere). After that, the
polymer stabilization treatment may be performed. In the liquid crystal
display device including a blue phase liquid crystal layer, the thickness
of the liquid crystal layer (cell thickness) is large in many cases.
Thus, when the first substrate 100 and the second substrate 108 are
attached to each other with the use of the photocurable and thermosetting
second sealant 104 with a high viscosity, even if the substrates are
exposed to the atmosphere from the reduced-pressure atmosphere, adhesion
between the substrates can be kept and a vacuum state can be kept on an
inner side than the sealant.

[0061]Furthermore, when the second sealant 104 is formed so as to form a
frame, a region between the first sealant 102 and the second sealant 104
can be in a vacuum state as well even if the substrates are exposed to
the atmosphere. In this case, even if the viscosity of the first sealant
102 is low and adhesion is not sufficient when the substrates are exposed
to the atmosphere after being attached to each other, a vacuum state can
be kept on an inner side than the first sealant 102 and the liquid
crystal can spread to the region which is in contact with the first
sealant 102 finally.

[0062]In addition, when heat treatment is performed in polymer
stabilization treatment, the viscosity of the liquid crystal layer 110 is
reduced. Accordingly, even when the liquid crystal layer 110 does not
spread over the entire surface on an inner side than the first sealant
102 at the stage of FIG. 1C, the liquid crystal layer 110 can spread to
the region which is in contact with the first sealant 102 in the heat
treatment in the polymer stabilization treatment. Note that the viscosity
of the second sealant 104 (a second sealant 114 in FIG. 1D) is reduced
and the width of the second sealant 104 is increased in the heat
treatment in the polymer stabilization treatment in some cases.

[0063]When the polymer stabilization treatment is performed, the
temperature range where the liquid crystal layer 112 exhibits a blue
phase can be widened.

[0064]Note that the second sealant 114 may be cured at the same time as a
step of light irradiation in the polymer stabilization treatment.

[0065]Next, heat treatment is performed to post-cure the first sealant 102
(see FIG. 1E). In the case where the second sealant 114 is irradiated
with light to be pre-cured in FIG. 1D, the second sealant 114 can also be
post-cured at the same time through this heat treatment. As a result, a
post-cured first sealant 116 and a post-cured second sealant 118 can be
obtained.

[0066]Note that the first sealant 102 may be post-cured in the heat
treatment in the polymer stabilization treatment. In this case, the heat
treatment step (the step of FIG. 1E) can be omitted; thus, the
manufacturing process can be simplified.

[0067]Next, the first substrate 100 and the second substrate 108 which are
attached to each other are cut (see FIG. 1F). Here, the first substrate
100 and the second substrate 108 can be cut between the post-cured first
sealant 116 and the post-cured second sealant 118. That is, in this
embodiment, even when the width of the second sealant 104 is increased
due to the polymer stabilization treatment which is performed before the
photocurable and thermosetting second sealant 104 is irradiated with
ultraviolet rays, the second sealant 104 can be removed. This is because
the second sealant 104 does not seal in the liquid crystal layer 112
directly.

[0068]Note that in the step of cutting the substrates, which is
illustrated in FIG. 1F, the substrates may be partly cut in consideration
of attachment of an FPC and the like. In this case, a liquid crystal
display device in which the second sealant 118 is partly formed is
manufactured in some cases.

[0069]As illustrated in FIGS. 1A to 1F, the photocurable and thermosetting
second sealant is formed on an outer side than the thermosetting first
sealant and made to serve for improvement of adhesion between the
substrates, whereby irradiation with ultraviolet rays for pre-curing the
second sealant is not needed. Accordingly, irradiation with ultraviolet
rays for pre-curing the second sealant is not performed on the liquid
crystal material before the liquid crystal material is subjected to
polymer stabilization treatment; thus, a liquid crystal display device
including a liquid crystal layer which exhibits a stable blue phase can
be manufactured. In addition, even in the case where polymer
stabilization treatment is performed before the photocurable and
thermosetting second sealant is irradiated with ultraviolet rays, when a
thermosetting sealant is used as the first sealant which is in contact
with the liquid crystal layer and the photocurable and thermosetting
second sealant is formed on an outer side than the first sealant,
adhesion between the substrates can be kept (a vacuum state can be kept
on an inner side than the sealant) even when the substrates are exposed
to the atmosphere from a reduced-pressure atmosphere, and increase in the
width of the first sealant which is in contact with the liquid crystal
layer can be suppressed.

Modified Example

[0070]FIGS. 1A to 1F illustrate a case where the first sealant 102 is
post-cured after polymer stabilization treatment; however, this
embodiment is not limited to such a manner. For example, as illustrated
in FIGS. 2A to 2F, the second substrate 108 and the first substrate 100
provided with the first sealant 102 may be attached to each other, the
second sealant 104, and the liquid crystal material 106 (see FIGS. 2A to
2C), and then heat treatment may be performed to post-cure the first
sealant 102 (see FIG. 2D). After that, polymer stabilization treatment
may be performed (see FIG. 2E). That is, FIGS. 2A to 2F illustrate a case
where the order of the step in FIG. 1D is replaced with the order of the
step in FIG. 1E in the steps illustrated in FIGS. 1A to 1F.

[0071]Note that FIGS. 2A to 2F illustrate a case where the substrates are
cut after polymer stabilization treatment (see FIG. 2F); however, the
substrates may be cut in a period after the first sealant 102 is
post-cured and before the polymer stabilization treatment is performed
(in a period between FIGS. 2D and 2E).

[0072]In addition, in this embodiment, a case where the first sealant 102,
the second sealant 104, and the liquid crystal material 106 are formed
over the first substrate 100 is described; however, this embodiment is
not limited to such a manner. For example, the first sealant 102 and the
second sealant 104 may be formed over the first substrate 100, and the
liquid crystal material 106 may be formed over the second substrate 108.
Then, the substrates may be attached to each other. Alternatively, the
first sealant 102 and the liquid crystal material 106 may be formed over
the first substrate 100, and the second sealant 104 may be formed over
the second substrate 108. Then, the substrates may be attached to each
other. Further alternatively, the first sealant 102 may be formed over
the first substrate 100, and the second sealant 104 and the liquid
crystal material 106 may be formed over the second substrate 108. Then,
the substrates may be attached to each other.

[0073]In addition, an element such as a transistor included in a liquid
crystal display device may be formed in advance over the first substrate
100 or the second substrate 108.

[0074]Moreover, in this embodiment, a case where the second sealant 104 is
formed on an outer side than the first sealant 102 so that the sealants
are formed so as to form a double frame is described; however, this
embodiment is not limited to such a manner. Either or both of a
thermosetting sealant and a photocurable and thermosetting sealant may be
formed between the first sealant 102 and the second sealant 104 so that
the sealants are formed so as to form a triple or more frame.

[0075]This embodiment can be implemented in combination with any of the
structures described in the other embodiments as appropriate.

Embodiment 2

[0076]In this embodiment, a method for manufacturing liquid crystal
display devices, which is different from the method in Embodiment 1, is
described with reference to drawings. Specifically, a step of taking out
a plurality of panels (obtaining a plurality of panels) from one panel is
described. Note that the manufacturing method described in this
embodiment has a lot in common with those in FIGS. 1A to 1F and FIGS. 2A
to 2F. Therefore, description of common portions is omitted and different
portions are described below.

[0077]First, the first substrate 100 is prepared and a plurality of first
sealants 102a, 102b, 102c, and 102d is formed over the first substrate
100 (see FIG. 3A).

[0078]The first sealants 102a to 102d can be formed using a thermosetting
sealant. The description of the first sealant 102 in Embodiment 1 can be
referred to for details of materials used for the first sealants 102a to
102d and the like; therefore, the description thereof is omitted here.

[0079]Further, after the first sealants 102a to 102d are formed over the
first substrate 100, the first sealants 102a to 102d may be pre-cured
through heat treatment. By pre-curing the first sealants 102a to 102d,
mixture of an impurity into a liquid crystal can be suppressed when the
liquid crystal is in contact with the first sealants 102a to 102d later.

[0080]Next, the photocurable and thermosetting second sealant 104 is
formed over the first substrate 100 and on an outer side than the first
sealant 102, and liquid crystal materials 106a to 106d are dropped on the
inner side than the first sealants 102a to 102d (on the inner side than
the frames) (see FIG. 3B).

[0081]The second sealant 104 can be formed so as to surround the first
sealants 102a to 102d. The second sealant 104 is formed so as to surround
the first sealants 102a to 102d, whereby adhesion between the substrates
can be improved.

[0082]The second sealant 104 serves for improvement of adhesion between
substrates at the time of attachment of the substrates. Therefore, the
viscosity of a resin used for the second sealant 104 is made higher than
those of resins used for the first sealants 102a to 102d.

[0083]A liquid crystal material which exhibits a blue phase can be used
for the liquid crystal materials 106a to 106d. The description of the
liquid crystal material 106 in Embodiment 1 can be referred to for
details of materials used for the liquid crystal materials 106a to 106d
and the like; therefore, the description thereof is omitted here.

[0084]Moreover, FIG. 3B illustrates a case where one droplet of the liquid
crystal materials 106a to 106d is dropped on the inner side than the
first sealants 102a to 102d. Note that this embodiment is not limited to
such a manner, and appropriate amounts of the liquid crystal materials
may be dropped at appropriate places on the inner side than the first
sealants 102a to 102d.

[0085]In FIG. 3B, the order of steps of forming the second sealant 104 and
dropping the liquid crystal materials 106a to 106d is not limited;
however, it is preferable that the second sealant 104 be formed and then
the liquid crystal materials 106a to 106d be dropped.

[0086]Next, the first substrate 100 and the second substrate 108 are
attached to each other (see FIG. 3C). The first substrate 100 and the
second substrate 108 can be attached to each other with the use of the
first sealants 102a to 102d and the second sealant 104.

[0087]When the first substrate 100 and the second substrate 108 are
attached to each other, the dropped liquid crystal materials 106a to 106d
spread over the substrate surface; thus, liquid crystal layers 110a to
110d are formed. The viscosity of the liquid crystal materials 106a to
106d is high because the liquid crystal materials 106a to 106d each
include a chiral agent. Accordingly, the liquid crystal layers 110a to
110d do not necessarily spread over the entire surfaces on the inner side
than the first sealants 102a to 102d (the liquid crystal layers 110a to
110d are not necessarily in contact with the first sealants 102a to
102d).

[0088]In addition, the first substrate 100 and the second substrate 108
are preferably attached to each other in a reduced-pressure atmosphere.
When the substrates are attached to each other in a reduced-pressure
atmosphere, even if the substrates are exposed to the atmosphere after
attachment, a vacuum state can be kept on the inner side than the
sealants and the liquid crystal can finally spread to be in contact with
the sealant.

[0089]Next, heat treatment is performed to post-cure the first sealants
102a to 102d (see FIG. 3D). As a result, post-cured first sealants 116a
to 116d can be obtained. The heat treatment can be performed in a
reduced-pressure atmosphere or in the normal air atmosphere.

[0090]Moreover, the viscosity of the liquid crystal layers 110a to 110d is
reduced through this heat treatment, and the liquid crystal layers 110a
to 110d can spread to the regions which are in contact with the first
sealants 116a to 116d. Note that the viscosity of the second sealant 104
(the second sealant 114 in FIG. 3D) is reduced and the width of the
second sealant 104 is increased in the heat treatment in some cases.

[0091]Next, the first substrate 100 and the second substrate 108 which are
attached to each other are cut (see FIG. 3E). Here, the first substrate
100 and the second substrate 108 can be cut between the post-cured first
sealant 116 and the second sealant 114.

[0092]Next, the liquid crystal layers 110a to 110d which are provided for
liquid crystal display panels 120a to 120d, which are separated from each
other, are subjected to polymer stabilization treatment to form liquid
crystal layers 112a to 112d (see FIG. 3F).

[0093]As illustrated in FIGS. 3A to 3F, in the case of obtaining a
plurality of panels from one panel, the substrates are cut and then the
cut substrates can be separately subjected to polymer stabilization
treatment. Accordingly, reduction in the size of an apparatus used for
light irradiation in the polymer stabilization treatment can be achieved,
and the liquid crystal layer can be uniformly irradiated with light. As a
result, a liquid crystal display device including a liquid crystal layer
which exhibits a stable blue phase can be manufactured. In particular, in
the case of obtaining a plurality of panels from one panel, large-sized
substrates are used as the first substrate 100 and the second substrate
108; thus, polymer stabilization treatment is preferably performed after
division.

[0094]This embodiment can be implemented in combination with any of the
structures described in the other embodiments as appropriate.

Embodiment 3

[0095]In this embodiment, a method for manufacturing a liquid crystal
display device, which is different from the methods in Embodiments 1 and
2, is described with reference to drawings.

[0096]First, the first substrate 100 is prepared and a sealant 202 is
formed over the first substrate 100 (see FIG. 4A).

[0097]The sealant 202 can be formed using a photocurable and thermosetting
resin. As the photocurable and thermosetting resin, a resin in which an
acrylic-based resin and an epoxy-based resin are mixed can be used.
Further, a UV initiator, a thermosetting agent, a coupling agent, or the
like is preferably mixed into the resin. Furthermore, a filler may be
mixed into the sealant 202.

[0098]Moreover, the sealant 202 may be formed so as to form a frame
(closed-loop shape). Here, a case where the sealant 202 is formed so as
to form a frame with a rectangular shape is described. Note that the
frame shape of the sealant 202 is not limited to the rectangular shape,
and the sealant 202 may be formed so as to form a frame with a circular
shape, an elliptical shape, a polygonal shape other than a rectangular
shape, or the like.

[0099]Next, the sealant 202 is irradiated with ultraviolet rays to be
pre-cured (see FIG. 4B). As a result, a pre-cured sealant 204 is
obtained. By pre-curing the sealant 202, mixture of an impurity into a
liquid crystal can be suppressed when the liquid crystal is in contact
with the sealant 204 later.

[0100]Then, the liquid crystal material 106 is dropped on an inner side
than the pre-cured sealant 204 (on an inner side than the frame of the
first sealant 204) (see FIG. 4C). By irradiating the sealant 202 with
ultraviolet rays to be pre-cured before formation of the liquid crystal
material 106, the liquid crystal material 106 can be prevented from being
irradiated with unintended light.

[0101]Next, the first substrate 100 and the second substrate 108 are
attached to each other (see FIG. 4D). The first substrate 100 can be
attached to the second substrate 108 with the use of the sealant 202.

[0102]When the first substrate 100 and the second substrate 108 are
attached to each other, the dropped liquid crystal material 106 spreads
over the substrate surface; thus, the liquid crystal layer 110 is formed.
The viscosity of the liquid crystal material 106 is high because the
liquid crystal material 106 includes a chiral agent. Accordingly, the
liquid crystal layer 110 does not necessarily spread over the entire
surface on an inner side than the pre-cured sealant 204 (the liquid
crystal layer 110 is not necessarily in contact with the pre-cured
sealant 204).

[0103]In addition, the first substrate 100 and the second substrate 108
are preferably attached to each other in a reduced-pressure atmosphere.
This is because when the substrates are attached to each other in a
reduced-pressure atmosphere, even if the substrates are exposed to the
atmosphere after attachment, a vacuum state can be kept on an inner side
than the sealant and the liquid crystal can finally spread to end
portions of the sealant (the liquid crystal can be formed in contact with
the sealant).

[0104]Next, polymer stabilization treatment is performed on the liquid
crystal layer 110 to form the liquid crystal layer 112 (see FIG. 4E).

[0105]When heat treatment is performed in the polymer stabilization
treatment, the viscosity of the liquid crystal layer 110 is reduced.
Accordingly, in FIG. 4D, even when the liquid crystal layer 110 does not
spread over the entire surface on an inner side than the pre-cured
sealant 204, the liquid crystal layer 110 can spread to the region which
is in contact with the pre-cured sealant 204 in the heat treatment in the
polymer stabilization treatment.

[0106]When the polymer stabilization treatment is performed, the
temperature range where the liquid crystal layer 112 exhibits a blue
phase can be widened.

[0107]Next, heat treatment is performed to post-cure the sealant 202 (see
FIG. 4F). As a result, a post-cured sealant 218 can be obtained.

[0108]Note that the pre-cured sealant 204 may be post-cured in the heat
treatment in the polymer stabilization treatment. In this case, the heat
treatment step (the step of FIG. 4F) can be omitted; thus, a
manufacturing process can be simplified.

[0109]Through the above steps, a liquid crystal display device including a
blue phase liquid crystal layer can be manufactured.

[0110]Note that in the steps in FIGS. 4A to 4F, the pre-cured sealant 204
may be subjected to heat treatment to be post-cured before the polymer
stabilization treatment. In this case, a structure where the order of the
step in FIG. 4E is replaced with the order of the step in FIG. 4F can be
obtained.

[0111]Further, heat treatment in the polymer stabilization treatment and
heat treatment for post-curing the pre-cured sealant 204 may be performed
at the same time. In this case, the number of heat treatment steps can be
reduced.

[0112]Furthermore, FIGS. 4A to 4F illustrate a case where the sealant 202
and the liquid crystal material 106 are formed over the first substrate
100; however, this embodiment is not limited to such a manner. For
example, the sealant 202 may be formed over the first substrate 100, the
liquid crystal material 106 may be formed over the second substrate 108,
and then the first substrate 100 and the second substrate 108 may be
attached to each other.

[0113]As illustrated in FIGS. 4A to 4F, even when a liquid crystal
dropping method is performed using a photocurable and thermosetting
sealant, the sealant 202 is irradiated with ultraviolet rays to be
pre-cured before formation of the liquid crystal material 106, whereby
the liquid crystal material 106 can be prevented from being irradiated
with unintended light. As a result, a liquid crystal display device
including a liquid crystal layer which exhibits a stable blue phase can
be manufactured. In addition, the sealant is irradiated with ultraviolet
rays to be pre-cured before heat is applied to the sealant, whereby it is
possible to suppress the increase in the width of the photocurable and
thermosetting sealant.

<Step of Obtaining a Plurality of Panels from One Panel>

[0114]Next, a case where the method illustrated in FIGS. 4A to 4F is used
in a step of taking out a plurality of panels (obtaining a plurality of
panels) from one panel is described with reference to FIGS. 5A to 5F.
Note that the manufacturing method illustrated in FIGS. 5A to 5F has a
lot in common with that in FIGS. 4A to 4F. Therefore, description of
common portions is omitted and different portions are described below.

[0115]First, the first substrate 100 is prepared, and a plurality of
sealants 202a to 202d is formed over the first substrate 100 (see FIG.
5A).

[0116]The sealants 202a to 202d can be each formed using a photocurable
and thermosetting resin. The description of the sealant 202 illustrated
in FIGS. 4A to 4F can be referred to for details such as materials used
for the sealants 202a to 202d; therefore, the description thereof is
omitted here.

[0117]Next, the sealants 202a to 202d are irradiated with ultraviolet rays
to be pre-cured, and then the liquid crystal materials 106a to 106d are
dropped on the inner side than pre-cured sealants 204a to 204d (on the
inner side than the frames) (see FIG. 5B).

[0118]Then, the first substrate 100 and the second substrate 108 are
attached to each other (see FIG. 5C). The first substrate 100 and the
second substrate 108 can be attached to each other with the use of the
sealants 202a to 202d.

[0119]When the first substrate 100 and the second substrate 108 are
attached to each other, the dropped liquid crystal materials 106a to 106d
spread over the substrate surface; thus, the liquid crystal layers 110a
to 110d are formed. The viscosity of the liquid crystal materials 106a to
106d is high because the liquid crystal materials 106a to 106d each
include a chiral agent. Accordingly, the liquid crystal layers 110a to
110d do not necessarily spread over the entire surfaces on the inner side
than the sealants 202a to 202d.

[0120]In addition, the first substrate 100 and the second substrate 108
are preferably attached to each other in a reduced-pressure atmosphere.

[0121]Next, heat treatment is performed to post-cure the sealants 204a to
204d (see FIG. 5D). As a result, post-cured sealants 218a to 218d can be
obtained. The heat treatment can be performed in a reduced-pressure
atmosphere or in the normal air atmosphere.

[0122]Moreover, the viscosity of the liquid crystal layers 110a to 110d is
reduced through this heat treatment, and the liquid crystal layers 110a
to 110d can spread to regions which are in contact with the sealants 218a
to 218d.

[0123]Next, the first substrate 100 and the second substrate 108 which are
attached to each other are cut (see FIG. 5E). Here, the first substrate
100 and the second substrate 108 can be cut between the post-cured
sealants 218a and 218b, sealants 218b and 218c, sealants 218c and 218d,
and sealants 218a and 218d.

[0124]Next, the liquid crystal layers 110a to 110d which are provided for
liquid crystal display panels 220a to 220d which are separated from each
other are subjected to polymer stabilization treatment to form liquid
crystal layers 112a to 112d (see FIG. 5F).

[0125]As illustrated in FIGS. 5A to 5F, in the case of obtaining a
plurality of panels from one panel, the substrates are cut and then the
cut substrates are separately subjected to polymer stabilization
treatment. Accordingly, reduction in the size of an apparatus used for
light irradiation in the polymer stabilization treatment can be achieved,
and the liquid crystal layer can be uniformly irradiated with light. As a
result, a liquid crystal display device including a liquid crystal layer
which exhibits a stable blue phase can be manufactured. In particular, in
the case of obtaining a plurality of panels from one panel, large-sized
substrates are used as the first substrate 100 and the second substrate
108; thus, polymer stabilization treatment is preferably performed after
division.

[0126]This embodiment can be implemented in combination with any of the
structures described in the other embodiments as appropriate.

Embodiment 4

[0127]In this embodiment, an example of the liquid crystal display device
which is manufactured in Embodiment 1, 2, or 3 is described with
reference to drawings.

[0128]FIGS. 6A1 and 6A2 are top views of panels in which transistors 4010
and 4011 and a liquid crystal element 4013 which are formed over a first
substrate 4001 are sealed between the first substrate 4001 and a second
substrate 4006 with a sealant 4005. FIG. 6B is a cross-sectional view
taken along line M-N of FIGS. 6A1 and 6A2.

[0129]The sealant 4005 is provided so as to surround a pixel portion 4002
and a scan line driver circuit 4004 which are provided over the first
substrate 4001. In addition, the second substrate 4006 is provided over
the pixel portion 4002 and the scan line driver circuit 4004. The pixel
portion 4002 and the scan line driver circuit 4004 are sealed between the
first substrate 4001 and the second substrate 4006 with the sealant 4005
together with a liquid crystal layer 4008 which exhibits a blue phase. In
the case where Embodiment 1 or 2 is applied, the sealant 4005 is formed
using a thermosetting resin. In the case where Embodiment 3 is applied,
the sealant 4005 is formed using a photocurable and thermosetting resin.

[0130]In FIG. 6A1, a signal line driver circuit 4003 which is formed over
a substrate separately prepared using a single crystal semiconductor film
or a polycrystalline semiconductor film is mounted in a region which is
different from the region surrounded by the sealant 4005 formed over the
first substrate 4001. In contrast, FIG. 6A2 illustrates an example in
which part of a signal line driver circuit is formed over the first
substrate 4001 with the use of a thin film transistor which includes an
oxide semiconductor. A signal line driver circuit 4003b is formed over
the first substrate 4001 and a signal line driver circuit 4003a which is
formed using a single crystal semiconductor film or a polycrystalline
semiconductor film is mounted on the substrate separately prepared.

[0131]Note that there is no particular limitation on the connection method
of a driver circuit which is separately formed, and a COG method, a wire
bonding method, a TAB method, or the like can be used. FIG. 6A1
illustrates an example of mounting the signal line driver circuit 4003 by
a COG method, and FIG. 6A2 illustrates an example of mounting the signal
line driver circuit 4003 by a TAB method.

[0132]Further, the pixel portion 4002 and the scan line driver circuit
4004 provided over the first substrate 4001 each include a plurality of
transistors. FIG. 6B illustrates the transistor 4010 included in the
pixel portion 4002 and the transistor 4011 included in the scan line
driver circuit 4004. Insulating layers 4020 and 4021 are provided over
the transistors 4010 and 4011.

[0133]Various kinds of transistors can be applied to the transistors 4010
and 4011 without particular limitation. A semiconductor formed using
silicon (for example, amorphous silicon, microcrystalline silicon, or
polysilicon) or an oxide semiconductor or the like can be used for a
channel layer of each of the transistors 4010 and 4011.

[0134]In addition, a pixel electrode layer 4030 and a common electrode
layer 4031 are provided over the first substrate 4001, and the pixel
electrode layer 4030 is electrically connected to the transistor 4010.
The liquid crystal element 4013 includes the pixel electrode layer 4030,
the common electrode layer 4031, and the liquid crystal layer 4008.

[0135]In a liquid crystal display device including the liquid crystal
layer 4008 which exhibits a blue phase, a method in which the gray scale
is controlled by generating an electric field generally parallel (i.e.,
in a lateral direction) to a substrate to move liquid crystal molecules
in a plane parallel to the substrate can be used. For such a method, an
electrode structure used in a plane switching (IPS) mode illustrated in
FIGS. 6A1 and 6A2 and FIG. 6B is employed in this embodiment. Note that
without limitation to an IPS mode, an electrode structure used in a
fringe field switching (FFS) mode can also be employed.

[0136]As the first substrate 4001 and the second substrate 4006, glass,
plastic, or the like having a light-transmitting property can be used. As
plastic, polyether sulfone (PES), polyimide, a fiberglass-reinforced
plastic (FRP) plate, a polyvinyl fluoride (PVF) film, a polyester film,
or an acrylic resin film can be used. Further, a sheet in which aluminum
foil is sandwiched between PVF films or polyester films can also be used.

[0137]Furthermore, a columnar spacer 4035 which is provided in order to
control the thickness (a cell gap) of the liquid crystal layer 4008 can
be obtained by selective etching of an insulating film. Note that a
spherical spacer may be used instead of the columnar spacer 4035.

[0138]In FIGS. 6A1 and 6A2 and FIG. 6B, a light-blocking layer 4034 is
provided on the second substrate 4006 side so as to cover the transistors
4010 and 4011. With provision of the light-blocking layer 4034, the
advantageous effect of stabilizing the thin film transistors can be
increased. The light-blocking layer 4034 may be provided over the first
substrate 4001. In this case, when polymer stabilization is performed by
irradiation with ultraviolet rays from the second substrate 4006 side, a
liquid crystal over the light-blocking layer 4034 can also be
polymer-stabilized when it exhibits a blue phase.

[0139]The light-blocking layer 4034 may be covered with the insulating
layer 4020 which functions as a protective film of the transistors;
however, there is no particular limitation.

[0140]Note that the protective film is provided to prevent entry of
contaminant impurities floating in the air, such as an organic substance,
a metal substance, or moisture, and is preferably a dense film. The
protective film may be formed by a sputtering method to have a
single-layer structure or a stacked-layer structure including any of a
silicon oxide film, a silicon nitride film, a silicon oxynitride film, a
silicon nitride oxide film, an aluminum oxide film, an aluminum nitride
film, an aluminum oxynitride film, and an aluminum nitride oxide film.

[0141]After the protective film is formed, the semiconductor layer may be
subjected to annealing (300° C. to 400° C.).

[0143]A conductive composition containing a conductive high-molecular
compound (also referred to as a conductive polymer) can also be used for
each of the pixel electrode layer 4030 and the common electrode layer
4031.

[0144]Further, a variety of signals and potentials are supplied, from an
FPC 4018, to the signal line driver circuit 4003 which is formed
separately, the scan line driver circuit 4004, or the pixel portion 4002.

[0145]Further, since the transistor is easily broken by static electricity
and the like, a protection circuit for protecting the driver circuits is
preferably provided over the same substrate for a gate line or a source
line. The protection circuit is preferably formed using a nonlinear
element in which an oxide semiconductor is used.

[0146]In FIGS. 6A1 and 6A2 and FIG. 6B, a connection terminal electrode
4015 is formed using the same conductive film as the pixel electrode
layer 4030, and a terminal electrode 4016 is formed using the same
conductive film as the source and drain electrode layers of the
transistors 4010 and 4011.

[0147]The connection terminal electrode 4015 is electrically connected to
a terminal included in the FPC 4018 through an anisotropic conductive
film 4019.

[0148]Although FIGS. 6A1 and 6A2 and FIG. 6B illustrate an example in
which the signal line driver circuit 4003 is formed separately and
mounted on the first substrate 4001, this embodiment is not limited to
such a structure. The scan line driver circuit may be formed separately
and then mounted, or only part of the signal line driver circuit or part
of the scan line driver circuit may be formed separately and then
mounted.

[0149]FIG. 7 illustrates an example of a cross-sectional structure of a
liquid crystal display device in which an element substrate 2600 and a
counter substrate 2601 are attached to each other with a sealant 2602,
and an element layer 2603 including a transistor or the like and a liquid
crystal layer 2604 are provided between the substrates.

[0150]In the case where color display is performed, light-emitting diodes
which emit light of plural colors are arranged in a backlight portion. In
the case of an RGB mode, a red light-emitting diode 2910R, a green
light-emitting diode 2910G, and a blue light-emitting diode 2910B are
disposed in each of a plurality of regions into which a display area of
the liquid crystal display device is divided.

[0151]A polarizing plate 2606 is provided on the outer side of the counter
substrate 2601, and a polarizing plate 2607 and an optical sheet 2613 are
provided on the outer side of the element substrate 2600. A light source
is formed using the red light-emitting diode 2910R, the green
light-emitting diode 2910G, the blue light-emitting diode 2910B, and a
reflective plate 2611. An LED control circuit 2912 provided over a
circuit substrate 2612 is connected to a wiring circuit portion 2608
provided over the element substrate 2600 through a flexible wiring board
2609 and further provided with an external circuit such as a control
circuit or a power source circuit.

[0152]The LEDs are individually made to emit light by the LED control
circuit 2912; thus, a field-sequential liquid crystal display device can
be realized.

[0153]This embodiment can be implemented in combination with any of the
structures described in the other embodiments as appropriate.

Embodiment 5

[0154]A liquid crystal display device disclosed in this specification can
be applied to a variety of electronic devices (including a game machine).
Examples of electronic devices include television sets (also referred to
as televisions or television receivers), monitors of computers or the
like, cameras such as digital cameras or digital video cameras, digital
photo frames, mobile phones (also referred to as cellular phones or
mobile phone sets), portable game consoles, portable information
terminals, audio reproducing devices, large-sized game machines such as
pachinko machines, and the like.

[0155]FIG. 8 illustrates an example of a television set 9600. In the
television set 9600, a display portion 9603 is incorporated in a housing
9601. Images can be displayed on the display portion 9603. Here, the
housing 9601 is supported by a stand 9605.

[0156]The television set 9600 can be operated with an operation switch of
the housing 9601 or a separate remote controller 9610. Channels and
volume can be controlled with operation keys 9609 of the remote
controller 9610 so that an image displayed on the display portion 9603
can be controlled. Moreover, the remote controller 9610 may be provided
with a display portion 9607 for displaying data output from the remote
controller 9610.

[0157]Note that the television set 9600 is provided with a receiver, a
modem, and the like. With the use of the receiver, general television
broadcasting can be received. Moreover, when the television set 9600 is
connected to a communication network by wired or wireless connection via
the modem, one-way (from a transmitter to a receiver) or two-way (between
a transmitter and a receiver, between receivers, or the like) data
communication can be performed.

[0158]FIG. 9A illustrates a portable game machine including a housing 9881
and a housing 9891 which are jointed with a connector 9893 so as to be
able to open and close. A display portion 9882 and a display portion 9883
are incorporated in the housing 9881 and the housing 9891, respectively.
The portable game machine illustrated in FIG. 9A additionally includes a
speaker portion 9884, a storage medium insertion portion 9886, an LED
lamp 9890, an input means (operation keys 9885, a connection terminal
9887, a sensor 9888 (a sensor having a function of measuring force,
displacement, position, speed, acceleration, angular speed, the number of
rotations, distance, light, liquid, magnetism, temperature, chemical
substance, sound, time, hardness, electric field, current, voltage,
electric power, radiation, flow rate, humidity, tilt angle, vibration,
smell, or infrared ray), a microphone 9889), and the like. It is needless
to say that the structure of the portable game machine is not limited to
the above structure and other structures provided with at least a liquid
crystal display device disclosed in this specification may be employed.
The portable game machine may include other accessory equipments as
appropriate. The portable game machine illustrated in FIG. 9A has a
function of reading out a program or data stored in a storage medium to
display it on the display portion, and a function of sharing information
with another portable game machine by wireless communication. The
portable game machine in FIG. 9A can have various functions without
limitation to the above.

[0159]FIG. 9B illustrates an example of a slot machine 9900 which is a
large-sized game machine. In the slot machine 9900, a display portion
9903 is incorporated in a housing 9901. In addition, the slot machine
9900 further includes an operation means such as a start lever or a stop
switch, a coin slot, a speaker, and the like. It is needless to say that
the structure of the slot machine 9900 is not limited to the above
structure, and another structure provided with at least the liquid
crystal display device disclosed in this specification may be employed.
The slot machine may include another accessory equipment as appropriate

[0160]FIG. 10A illustrates an example of a mobile phone 1000. The mobile
phone 1000 is provided with a display portion 1002 incorporated in a
housing 1001, operation buttons 1003, an external connection port 1004, a
speaker 1005, a microphone 1006, and the like.

[0161]When the display portion 1002 of the mobile phone 1000 illustrated
in FIG. 10A is touched with a finger or the like, data can be input into
the mobile phone 1000. Furthermore, operations such as making calls and
composing mails can be performed by touching the display portion 1002
with a finger or the like.

[0162]There are mainly three screen modes of the display portion 1002. The
first mode is a display mode mainly for displaying an image. The second
mode is an input mode mainly for inputting information such as text. The
third mode is a display-and-input mode in which two modes of the display
mode and the input mode are mixed.

[0163]For example, in the case of making a call or composing a mail, a
text input mode mainly for inputting text is selected for the display
portion 1002 so that text displayed on a screen can be input. In this
case, it is preferable to display a keyboard or number buttons on almost
all the area of the screen of the display portion 1002.

[0164]When a detection device including a sensor for detecting
inclination, such as a gyroscope or an acceleration sensor, is provided
inside the mobile phone 1000, display on the screen of the display
portion 1002 can be automatically switched by determining the direction
of the mobile phone 1000 (whether the mobile phone 1000 is placed
horizontally or vertically).

[0165]The screen mode is switched by touching the display portion 1002 or
operating the operation buttons 1003 of the housing 1001. Alternatively,
the screen mode can be switched depending on the kind of images displayed
on the display portion 1002. For example, when a signal of an image
displayed on the display portion is moving image data, the screen mode is
switched to the display mode. When the signal is text data, the screen
mode is switched to the input mode.

[0166]Furthermore, in the input mode, when input by touching the display
portion 1002 is not performed for a certain period while a signal is
detected by the optical sensor in the display portion 1002, the screen
mode may be controlled so as to be switched from the input mode to the
display mode.

[0167]The display portion 1002 can also function as an image sensor. For
example, an image of a palm print, a fingerprint, or the like is taken by
touching the display portion 1002 with the palm or the finger, whereby
personal authentication can be performed. Furthermore, by providing a
backlight or a sensing light source emitting a near-infrared light for
the display portion, an image of a finger vein, a palm vein, or the like
can also be taken.

[0168]FIG. 10B also illustrates an example of a mobile phone. The mobile
phone illustrated in FIG. 10B includes a display device 9410 having a
display portion 9412 and operation buttons 9413 in a housing 9411 and a
communication device 9400 having operation buttons 9402, an external
input terminal 9403, a microphone 9404, a speaker 9405, and a
light-emitting portion 9406 which emits light when receiving a call in a
housing 9401. The display device 9410 having a display function can be
detached from or attached to the communication device 9400 having a
telephone function in two directions indicated by the arrows.
Accordingly, the display device 9410 and the communication device 9400
can be attached to each other along their short sides or long sides. In
addition, when only the display function is needed, the display device
9410 can be detached from the communication device 9400 and used alone.
Images or input information can be transmitted or received by wireless or
wired communication between the communication device 9400 and the display
device 9410, each of which has a rechargeable battery.

Example 1

[0169]In this example, a case where a liquid crystal display device is
manufactured using a liquid crystal dropping method is described.

[0170]First, spacers each having a diameter of 4 μm were dispersed over
a 5-inch glass substrate 500 (EAGLE 2000® manufactured by Corning
Incorporated), and then thermosetting first sealants 502a and 502b were
formed (see FIG. 11A). The thermosetting first sealants 502a and 502b
were each formed to have a rectangular shape of 4 cm by 3 cm.

[0171]The thermosetting first sealants 502a and 502b were formed using an
epoxy resin with a viscosity of 30 Pasec (at 25° C.).

[0172]Next, the glass substrate 500 over which the first sealants 502a and
502b are formed were subjected to heat treatment to be pre-cured. The
first sealants 502a and 502b were subjected to the heat treatment in an
oven at 90° C. for three hours.

[0173]Then, the glass substrate 500 was taken out from the oven and then
cooled to the room temperature (25° C.). After that, a
photocurable and thermosetting second sealant 504 was formed so as to
surround the first sealants 502a and 502b. The photocurable and
thermosetting second sealant 504 was formed to have an 11-cm-square
shape.

[0174]The photocurable and thermosetting second sealant 504 was formed
using a resin which has a viscosity of 300 Pasec (at 25° C.) and
includes an acrylic-based resin, an epoxy-based resin, a UV initiator, a
thermosetting agent, or a coupling agent.

[0175]Next, liquid crystal materials 506a and 506b were dropped on the
inner side than the first sealants 502a and 502b, respectively, over the
glass substrate 500 (see FIG. 11B). The liquid crystal materials 506a and
506 each include commercially available materials shown in Table 1.

[Table 1]

[0176]In this case, the temperature of the liquid crystal material was set
to 80° C. at which the liquid crystal material exhibits an
isotropic phase, and 4.8-mg droplets of the liquid crystal materials 506a
and 506b were dropped on the inner side than the first sealants 502a and
502b, respectively.

[0177]Then, a glass substrate 508 (EAGLE 2000® manufactured by Corning
Incorporated) was attached to the glass substrate 500. Here, the glass
substrate 508 was fixed to an upper side of a chamber with an
electrostatic chuck, and the glass substrate 500 on which the liquid
crystal material is dropped was placed on a lower side of the chamber.
Then, the pressure inside the chamber was reduced to 100 Pa, and the
glass substrate 500 and the glass substrate 508 were attached to each
other. After that, the chamber was exposed to the atmosphere (see FIG.
11C).

[0178]The distance between the glass substrate 500 and the glass substrate
508 was approximately 4 μm at this time. The liquid crystal materials
506a and 506b spread over approximately 90 percent of surfaces on the
inner side than the first sealants 502a and 502b, respectively, and
liquid crystal layers 510a and 510b were formed.

[0179]Next, the liquid crystal layers 510a and 510b were subjected to
polymer stabilization treatment to form liquid crystal layers 512a and
512b (see FIG. 11D). The polymer stabilization treatment was performed in
such a manner that after the liquid crystal layers 510a and 510b were
heated to 50° C., the temperature was decreased by one degree per
minute from 50° C. in order that a phase may transfer from an
isotropic phase to a blue phase, and then irradiation with ultraviolet
rays (1.5 mW/cm2) with a main wavelength of 365 nm was performed for
30 minutes while the temperature was kept at 36° C. at which the
blue phase spreads over the entire surface. In addition, through the heat
treatment in the polymer stabilization treatment, the liquid crystal
layers 510a and 510b spread over the entire surfaces on the inner side
than the first sealants 502a and 502b, respectively.

[0180]Then, heat treatment was performed to cure the thermosetting first
sealants 502a and 502b. As a result, post-cured first sealants 516a and
516b and a post-cured second sealant 518 were obtained (see FIG. 11E).
After that, the glass substrate 500 and the glass substrate 508 were cut
(see FIG. 11F) and the separated panels were each provided with an FPC or
the like, whereby a liquid crystal display device was manufactured. FIG.
13A is a photograph showing an appearance of an FPC in a state just after
attachment. Note that in this example, the phases of the liquid crystal
layers 512a and 512b transferred to an isotropic phase once through the
heat treatment for post-curing. However, as shown in a photograph of FIG.
13B, which is taken with a polarizing microscope (which is taken under
crossed nicols with a reflective polarizing microscope of 200
magnifications), it was confirmed that even in the case where the phases
of the entire surfaces of the liquid crystal layers transferred to an
isotropic phase once through the heat treatment for post-curing after the
polymer stabilization treatment, the liquid crystal layers 512a and 512b
each kept exhibiting a blue phase when the liquid crystal layers 512a and
512b were cooled to the room temperature (25° C.).

Example 2

[0181]In this example, a case where a liquid crystal display device is
manufactured using a photocurable and thermosetting resin as a sealant is
described.

[0182]First, spacers each having a diameter of 4 nm were dispersed over a
5-inch glass substrate 600 (EAGLE 2000® manufactured by Corning
Incorporated), and then photocurable and thermosetting sealants 602a,
602b, and 604 were formed (see FIG. 12A). The photocurable and
thermosetting sealants 602a and 602b were each formed to have a
rectangular shape of 4 cm by 3 cm. The photocurable and thermosetting
sealant 604 was formed to have an 11-cm-square shape.

[0183]The photocurable and thermosetting sealants 602a, 602b, and 604 were
formed using a resin which has a viscosity of 300 Pasec (at 25°
C.) and includes an acrylic-based resin, an epoxy-based resin, a UV
initiator, a thermosetting agent, and a coupling agent.

[0184]Next, the glass substrate 600 over which the sealants 602a, 602b,
and 604 are formed were irradiated with ultraviolet rays to be pre-cured.
As a result, pre-cured sealants 603a, 603b, and 605 were obtained (see
FIG. 12B). Irradiation with ultraviolet rays of 13 mW/cm2 with a
wavelength of 365 nm was performed using a Deep UV lamp with a main
wavelength of 250 nm to 400 nm for 0.2 seconds.

[0185]Next, one droplet of liquid crystal materials 606a and 606b was
dropped on the inner side than the sealants 603a and 603b, respectively,
over the glass substrate 600 (see FIG. 12C). Note that the liquid crystal
materials 606a and 606b each include commercially available materials
which are similar to those shown in Table 1 of Example 1.

[0186]In this case, the temperature of the liquid crystal material was set
to 80° C. at which the liquid crystal material exhibits an
isotropic phase, and one droplet (4.8 mg) of the liquid crystal materials
606a and 606b was dropped on the inner side than the sealants 603a and
603b, respectively.

[0187]Note that in the case of a panel, a plurality of droplets of the
liquid crystal materials is preferably dropped at a plurality of portions
because the liquid crystal materials spread uniformly over a panel
surface. Therefore, polymer stabilization treatment can be performed more
uniformly on the liquid crystal layers and generation of defects can be
prevented when an image is displayed.

[0188]Then, a glass substrate 608 (EAGLE 2000® manufactured by Corning
Incorporated) was attached to the glass substrate 600. Here, the glass
substrate 608 was fixed to an upper side of a chamber with an
electrostatic chuck, and the glass substrate 600 on which the liquid
crystal material is dropped was placed on a lower side of the chamber.
Then, the pressure inside the chamber was reduced to 100 Pa, and the
glass substrate 600 and the glass substrate 608 were attached to each
other. After that, the chamber was exposed to the atmosphere (see FIG.
12D).

[0189]The distance between the glass substrate 600 and the glass substrate
608 was approximately 4 μm at this time. The liquid crystal materials
606a and 606b spread over approximately 90 percent of surfaces on the
inner side than the sealants 603a and 603b, respectively, and liquid
crystal layers 610a and 610b were formed.

[0190]Next, the liquid crystal layers 610a and 610b were subjected to
polymer stabilization treatment to form liquid crystal layers 612a and
612b (see FIG. 12E). The polymer stabilization treatment was performed in
such a manner that after the liquid crystal layers 610a and 610b were
heated to 50° C., the temperature was decreased by one degree per
minute from 50° C. in order that a phase may transfer from an
isotropic phase to a blue phase, and then irradiation with ultraviolet
rays (1.5 mW/cm2) with a main wavelength of 365 nm was performed for
30 minutes while the temperature was kept at 36° C. at which the
blue phase spreads over the entire surface. In addition, through the heat
treatment in the polymer stabilization treatment, the liquid crystal
layers 610a and 610b spread over the entire surfaces on the inner side
than the sealants 603a and 603b, respectively.

[0191]Next, irradiation with ultraviolet rays of 13 mW/cm2 with a
wavelength of 365 nm was performed for 60 seconds and then heat treatment
was performed at 120° C. for 60 minutes in order to cure the
photocurable and thermosetting sealants 603a, 603b, and 605. As a result,
post-cured sealants 616a, 616b, and 618 were obtained (see FIG. 12F).
After that, the glass substrate 600 and the glass substrate 608 were cut
(see FIG. 12G) and the separated panels were each provided with an FPC or
the like, whereby a liquid crystal display device was manufactured. Note
that in this example, the phases of the liquid crystal layers 612a and
612b transferred to an isotropic phase once through the heat treatment
for post-curing the photocurable and thermosetting sealants 603a, 603b,
and 605. However, it was confirmed that even in the case where the phases
of the entire surfaces of the liquid crystal layers transferred to an
isotropic phase once through the heat treatment for post-curing after the
polymer stabilization treatment, the liquid crystal layers 612a and 612b
each kept exhibiting a blue phase when the liquid crystal layers 612a and
612b were cooled to the room temperature (25° C.).

[0192]This application is based on Japanese Patent Application serial no.
2009-131121 filed with Japan Patent Office on May 29, 2009, the entire
contents of which are hereby incorporated by reference.